As electronic devices and components are operating at higher and higher speeds and increasing frequency ranges, the packaging of the devices becomes an increasing cause of performance degradation. Therefore it is customary to mount semiconductor devices that operate at microwave frequencies directly onto the circuit substrate. This mounting process requires wire bonding or solder-bump mounting. These bonding and mounting techniques have several drawbacks and limitations. For example, the mounting substrate must be rigid for precise mounting and bonding, but such rigid substrates are expensive when large areas are included. In addition, the cost of the microwave device package is further increased due to low wire bond yields, If inverse-die solder bump mounting is used, it may require air cavities trenched onto the substrate to minimize radio frequency (RF) effects on the die circuitry. These trenches, however, are difficult to manufacture. Furthermore, the added inductive reactance of the bond wires requires precise mounting and manual adjustment for repeatable performance. The bond wires also radiate energy causing undesirable energy losses and undesirable cross talk.
There is clearly a need to package such high frequency devices in a surface mount package that can be machine picked and placed onto a printed circuit board. Typically, the interconnections on a printed circuit can maintain controlled impedance and critical connections can be shielded using ground planes and multi layered techniques. It is desirable, however, also to maintain controlled impedance throughout the integrated circuit (IC) package itself. For example, U.S. Pat. No. 5,323,533 to Christian Val (the '533 Patent) discloses a surface-mounted package whose wire bonds and leads have controlled impedance and a coaxial structure. However, the packaging described in the '533 Patent still has some limitations in high-frequency applications. In particular, a bond wire connects the electric component to a pad on the package periphery in the '533 Patent. That pad in turn extends to become the center lead of the package. It is difficult to maintain constant impedance along the bond-wire to pad transition. In addition, it is also difficult to completely shield this connection and it is difficult to maintain the mechanical precision of spacing between those leads, as each lead is extended separately from the main package and those leads tend to bend with mechanical stress of temperature changes.
Thus, its desirable to provide a high frequency packaging method and high frequency device package and it is to this end that the present invention is directed.